My Arab is doing 1-2 shows in dressage and showjumping every month, in the late summer and autumn some eventing as well. I adapt his feed schedule according to grazing time mostly. In winter we cannot turn our horses out in the field here (wet Netherlands) so he gets paddock playtime. During winter he gets full portions of hay twice a day, half a scoop of basic pellets twice a day, half a scoop of oat sports mix, and a small bucket of carrots. Additional supplements if necessary. In autumn and spring he is turned out in the field during the day, in summer pretty much all day, and when it gets hot 24/7. In those seasons he gets half a portion of hay in the morning and night, 1/4 scoop of basic pellets twice a day and half a scoop of oats sports mix.

Just a simple high fat high fibre grain and some salt maybe a few supplements if he needs it. More in the summer, less in the winter as it’s cold and he’s not getting worked as much and he doesn’t need the extra energy and I don’t want him fat 😂

My horses do eventing, so the nutrient and energy requirements are very important. They are followed by a professional to be sure their nutritional intakes are adapted to them. The ration depends of the horse's age, weight and diary activity. They have hay, specific pellets and vitamines. I do not know exactly the quantity of food my horses eat per day but roughly, it represents 2% of their weight in dry matter. They do not have a lot of lipid, unless they lose weight during the competition months. They have dietary supplements in reasonable amounts. We often check their level of phosphorus, sodium, magnesium, iron selenium... Roughly, they eat the same things throughout the year but we increase the doses in competition season and winter time.

Depends on a lot of factors. Most of my horses in the past have had steady diets season to season. This past winter, though, my retired show horse dropped quite a bit of weight when he began refusing to eat his hay (which I can't blame him for; hay around here sucks). When I first noticed it, I upped his regular feed, a 12% maintenance & light performance pellet. When that didn't work, I added alfalfa cubes. He decided he wasn't a fan of cubes, so I switched to alfalfa pellets, and that did the trick. We played with portion sizes for a couple months, then he returned to normal weight. I didn't add any weight-building supplements, though, because he's generally a VERY easy keeper/equine garbage disposal & I didn't want him to gain weight too fast.

That said, I live in Texas. Winters are mild. I have friends in northern states who up their hay in the winter to help the horses keep warm, but that's about it.